Piezoelectric unit and method of making same



May 4,1948. F. MASSA PIEZOBLECTRIC UNIT AND IBTHOD OF KING SAIB Filed Jan. 19, 1944 4 Sheets-Sheet 1 FIG. I

FIBE

FIG. 3

F. MASSA PIBZOELBOTRIG UNIT AND IBTHOD 0F IAKING SAIE May 4, 1948.

Filed Jan. 19, 1944 4 Sheets-Sheet 2 uvmvron hw /z Mum y 4, 1943- I F. MASSA 2,440,904

PIBZOBLECTRIG URI! AND IETHOD OF MAKING SAKS Filed Jan. 19, 1944 4 Sheets-Sheet 3 FIG. 12.

mmvrm F RANK Mnssn Arromvz May 4, 1948. F. MASSA mawm PIEZOELEGTEKIC UNIT AND METHOD OF MAKING SAW Filed Jan. 19,, 1944 4 Sheets-Sneak 4 JNVENTOR. FRANK M A ssA ATTORNEY Patented May 4, 1948 PIEZOELECTRIC UNIT AND METHOD OF MAKING SAME Frank Massa, Cleveland Heights, Ohio, assignor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Application January 19, 1944, Serial n 519,068

19 Claims. 1

My invention pertains to piezoelectric crystals and more particularly to along piezoelectric crystal and the method of making the same, and is a continuation in part of my application, Serial Number 454,136, which is abandoned.

An object of my invention is to provide a piezoelectric crystal plate or unit of the expander type which is long compared to the longest expander crystal plate or unit which can be obtained from a single out from a single crystal slab.

A further object of my invention is to provide a cheaper, faster, and more economical method oflcbtaining crystal plates from the virgin crysta s.

it is another object of my invention to provide a crystal unit which has a lower resonant freouency.

Another object of my invention is to provide a more sensitive piezoelectric crystal unit.

Still another object of my invention is to provide a piezoelectric crystal unit having a large capacity.

A further object oi my invention is to provide a method of cutting crystal plates from the virgin crystals which utilizes a larger proportion or the material in the crystals.

Another object oi my invention is to produce 45 degree cut expander plates from a virgin crystal of a length greater than could be obtained by a single cut through a ingle slab of crystalline material.

@ther objects and a fuller understanding of my invention may he had by referring to the follow ingdrawings, the detailed description, and the claims.

Figure 1 illustrates a virgin Rochelle salt crys tal.

Figure 2 illustrates sia'o cut from the virgin crystal and after several steps in the process of making my new crystal unit have been taken.

Figure 3 illustrates two crystal slabs which have been connected together to form a composite crystal slab.

Figure 4 illustrates an expander plate out from the composite crystal slab shown in Figure 3.

Figure 5 illustrates an expander unit made from the plate shown in Figure l.

Figure 6 illustrates a pair of crystal plates which have cut from a composite slab.

Figure 7 illustrates a bender unit made from a pair of plates such as is illustrated in Figure 6.

Figure 8 illustrates an expander unit cut from a composite slab according to my invention.

Figure 9 illustrates a typical virgin crystal of ammonium dihydrosen phosphate crystalline material, and how a slab may be cut therefrom.

Figure 10 illustrates a number of slabs connected together and how a plate may be out therefrom.

Figure 11 illustrates a crystal which has had its growth along its X-axis zorclbly increased.

Figure 12 shows how two or more slabs of crystalline material may be connected side-by-slde and out according to my invention.

Figure 13 is a plan view of a major race of a crystal of potassium tartrate.

Figure 14 is a sectional view taken along line iL-il of Figure 13,, and

Figure 15 is a view of several slabs of potassium tartrate crystalline material connected together and how it may he cut in accordance with my invention to obtain long plates.

My process produces a piezoelectrically active crystal unit of the bender or expander type which is longer than can he obtained by the present process, and comprises cutting longitudinal. slabs of crystalline material irom one or more of the virgin or mother crystals, and thereafter connecting the slahs together side-hy-side to establish a wide composite slalo from which plates can he cut, and then processing the plates to make piezo= electric units.

The virgin crystals of Rochelle salt, one of which is shown in Figure l and is indicated genorally by the reierence character it, are usually about 22 inches long, 3% inches wide. and 1% inches thicl; at the thickest point. A slab 9 which is suitable for making bender multiplate flexing elements and expander plates is cut from the crystal iii in accordance with the dotted lines. The thickness of the slab along the 2; axis clepends upon the desired dimension between the electrode faces of the finished unit. If this dimension is to be large only one slab t can he cut "from a crystal ill, but it the dimension is to he smaller then more one slats can he obtained from one crystal, and these slabs can be con.- nected side-hy-side instead of using slabs separate crystals.

After the slalihing operations have been 32eriormed the angular edge portions ii are cut oil to establish prepared connecting races it which extend in a direction substantially parallel to the Z orthogonal axis of the crystalline material. Uhviously this step could have been performed prior to the slabbing operation if it was so desired.

After a plurality of these crystal slabs such as V 9 and 83 have been obtained either from the same amaeoe than could be obtained in a single slab.

It is also within the scope of my invention that the slabs 9 and I3 can be connected together by means of cement on their broad faces to establish a composite crystal slab of greater thickness in the direction of the X axis.

The method of joining the two crystal slabs e and i3 may be by the Pfundt method disclosed in Patent 2,168,943, or it may be by any of the known cements such as Canada balsam or, for example, by melted Rochelle salt which cools after application and hardens to hold the two pieces of Rochelle salt crystal together.

After the two crystal slabs 9 and it; have been connected together side-by-side by means of cement on the connecting faces to establish a wide composite slab l5, they may be cut at an angle substantially 45 degrees to the Y and Z orthogonal axes to establish expander plates i8 and 26.

The orientation of the plates [6 and 28 with respect to the composite crystal slab I is shown by the dotted lines in Figure 3. The plate It is of a different orientation than the usual expander plate, and a, detailed description of its operation and its advantages may be found in my application Serial Number 431,429, now abandoned and refiled as Serial No. 631,667. Due to this different orientation it is necessary to electrode the plates on their thin edges, as is shown in Figure 5. This expander plate It may be sold in the form shown in Figure 4, or several further processing steps may be taken to establish an expander unit. These further steps include applying two electrodes H, i 8 on the crystal faces which are spaced apart along the X orthogonal axis of the crystalline material, and which are perpendicular to the X axis and parallel to both the Y and Z axes. Leads l9 and 20 may be applied to the crystal plate to complete the unit. These leads I9, 20 may be connected to the crystal plate prior to the electroding, or they may be connected to the electrode ll, I8 after they have been cemented to the crystal faces which are spaced apart along the X axis. One or more coats of waterproofing material may be added if the unit is to be used in a moist location. These leads I9, 20 are adapted to connect the unit in an electrical circuit, such for example as to an amplifier. The unit may be used as a microphone in which case it establishes an alternating potential across the electrodes in accordance with the alternating pressure which is applied to its faces, or the unit may be used as'a speaker in which case it establishes an alternating pressure in accordance with an alternating potential applied across the electrodes.

If the unit is going to be used as a motor device in which relatively high voltages will be applied between the electrodes l7 and i8 it may be n cessary to provide insulation 2! such as mica between one or more of the electrodes ll, It and the joint 22 which extends from one electrode to the other, as the material used for joining the two portions of crystal together may not be as good an insulator as the crystalline material.

The composite plate which is cut from my composite crystal slab has the property of expanding and contracting in two directions each at about 45 degrees to the Y and Z orthogonal axes. If two plates 23, 24 are cut from a bar of crystalline '4 material in such a manner that one will expand upon being subjected to a voltage of a first polarity, and the other will contract upon being subjected to a voltage of the same polarity, and the two plates are connected together face to face so that they mutually restrain and actuate each other, a bender multiplate flexing element construction results. For a more detailed description of this bender element reference may be had to my application Serial Number 431,429, which is abandoned. The advantage of the element made according to my present invention is that a much longer length may be obtained, and accordingly greater amplitude of movement of the crystal unit and its load may be realized.

As in the case of the expander unit it may be found advantageous to provide insulation 2i between the electrodes ll, i8 and the crystalline material.

With my method of construction great saving of time, labor, and materials is realized, and a crystal plate of any length may be obtained. The number of slabs such as 9 and it which can be connected together is practically unlimited.

The saving in labor over the old methods of making long expanders arises from cementing the slabs Q and I3 together before cutting out the plates, thereby substituting one operation of cementing two slabs together for a number of operations of cementing a plurality of small plates together.

The saving of material arises from the joint 22 between the two portions of crystalline material extending in a direction parallel to the Z orthogonal axis of the crystalline material instead of at a 45 degree angle to it thereby saving a triangle of material from each slab. A crystal expander plate made according to my process from two slabs of equal width is therefore more than twice as long as a plate made from one slab of material.

A more uniform crystal plate can be produced and its is easier and quicker to make one long joint than a number of small ones.

Another advantage of cementing the long slabs and of machining the composite slab is that it is relatively easy to produce a rectangular parallelepiped whereas by attempting to cement two small elements it would be virtually impossible to keep adjacent sides of the two plates in exactly the same plane unless very elaborate jigs were provided.

Among the advantages of using a plate or unit made according to my process is that due to the increased length the crystal will have a lower resonant frequency and will have a greater capacity. A further advantage lies in the fact that when it is used as a microphone it is more sensitive for a given capacity than would be possible from a shorter crystal plate or unit having a higher resonant frequency.

Figure 8 illustrates an expander plate 25 cut from a composite slab such as is illustrated in Figure 3, and electroded to make a piezoelectric expander unit. The unit comprises a first portion 21 from the slab It, a second portion 28 from the slab 9, cement means It between the portions, and electrode means 29, 30 on the large faces which are perpendicular to the X orthogonal axis of the crystalline material.

Leads iii, 32 are in engagement respectively with the electrodes 29, 36 for connecting the unit in an electrical circuit, and if it is desired insulation means may be placed between the electrodes 29, 30 and the face of the crystal plate at together before the slabbing operation.

wtion with the bender unit.

My invention is applicable to a great many crystalline materials such as quartz, primary ammonium phosphate, primary potassium hosphate, boracite, zinc blend (sphalerite), potassium phosphate, potassium tartrate, and others.

Figures 9 to 12 illustrate how it may be applied to ammonium dihydrogen phosphate, sometimes called primary ammonium phosphate, and henceforth in this application called ADP, and Figures 13 to 15 illustrate how it may be applied to potassium tartrate [Ka(C4H4Oe)'%HaO], sometimes called potassium d-tartrate hemihydrate.

Figure 9 illustrates a typical ammonium dihydrogen phosphate crystal II and shows how a slab 3| can be cut therefrom parallel to the X-Y axes and perpendicular to the Z axis. A number of slabs (ll may be connected together as was explained in detail in connection with Rochelle salt, and a large expander plate 32 out therefrom. Plates 32 out from the composite slab/3i at 45 degrees to the X-Y axes form expander plates. These large ADP expander plates may be sold as plates or they may be further treated by the application of electrodes, leads. insulating material and waterproofing material as in the case of Rochelle salt.

While my invention may be very useful with the typical ADP crystal shown in Figure 9. I have found it to be more useful for use with ADP crystals where the sideways growth (along the X-axis) has been exaggerated. Such a crystal 33 is shown in Figure 11, and a, slab 34 may be out from it as illustrated. A number of slabs 34 may be connected together side-by-side and one or more expander plates 35 of increased length cut from it as is shown in Figure 1?.

The side or connecting faces of th ADP crystal slabs st, 33 may not need to be cut or milled in order to prepare a smooth face ior connection to the side face of another crystal slab, as many of the ADP crystals which have been grown have smooth side i'aces, and when out into slabs the slabs have laces which are suitable for connection to a smooth face of another slab. It is also within the scope of my invention to connect the crystals (Rochelle salt, ADP, or any other typel ADP crystals are particularly adaptable and sometimes may even be connected without treating their side faces in any manner.

Figure i3 is a plan view of a typical crystal 38 of potassium tartrate showing its "beveled end faces, and Figure id is a section taken along line i l-44 showing its beveled minor side faces. These crystals have a tendency to grow thin, and may not need to be slabbed. Due to the beveled minor side faces it may be necessary to prepare cormecting faces in a manner similar to that described in connection with Rochelle salt crystals. Figure 15 shows a plurality 0? crystals or slabs from. crystals oi potassium tar-crate connected toe-ether, and illustrates how a large expander plate may he cut from the composite slab. Y

Multlgolate flexing elements may be made from the ADP and potassium tartrate crystals by com nesting together two plates cut with oliiierent orientation as has previously been explained in detail, and they would appear similar to the de vice shown in Figure 6. 7

Although I have described my invention with a certain degree of particularity, it is to be understood that the present disclosure has been made till 6 only by way 0! example and that numerous changes in the details or construction and the combination and arrangement or parts may be resorted to without departing from thespirit and scope of the invention as hereinafter claimed.

I claim as my invention:

1. The process of making a crystal unit comprising the steps of providing a plurality of crystal slabs, orienting said plurality of crystal slabs so that their like axes extend in the same directions, connecting said plurality of crystal slabs together to form a composite slab, cutting said composite slab to establish at least one composite crystal plate of a size larger than could have been obtained from a single cut or one crystal slab, and treating said composite crystal plate to-establish a crystal unit.

2. The process of making a crystal unit comprising the steps oi: providing a plurality of crystals of piezoelectrically active crystalline material each having first, second, and third orthogonal axes, slabbing said crystals by removing a portion of the crystalline material from each crystal to establish a prepared connecting race, orienting said plurality oi. crystal slabs so that each of said first, second, and third orthogonal axes is parallel to each of its like axes and no other, connecting said prepared crystal faces together to establish a composite slab of a large size, cutting said composite slab at substantially 45 degrees to one of said orthogonal axes to establish a composite crystal plate having crystalline material from more than one of said plurality of crystal slabs, and treating said composite crystal plate to establish a crystal unit,

3. The process of making a crystal unit comprising the steps oi: providing a plurality of crystals of piezoelectrically active material each having first, second, and third orthogonal axes, removing a portion of the crystalline material from each crystal to establish a plurality of slabs each having a prepared connecting face which is parallel to said third orthogonal axis, orienting said plurality of crystal slabs so that each of said first, second, and third orthogonal axes is parallel to each of its like axes and so that the connecting laces lie in a position from which they can be connected together, applying a cement to one or moreol said connecting laces, pressing said connecting faces together to establish a corn-= posits slab oi a large size, cutting said composite slab at an angle to two oi said orthogonal axes to establish a composi e crystal plate having crystalline material fronlinore than one or" said plurality of crystals, and treating said composite crystal plate to establish a crystal 4. The process of making a piezoelectric crystal unit of the Rochelle salt tyne comprising the steps of: providing a plurality of crystals of piezoelectrically active crystalline material each having an Y, and Z orthogonal axis, removing a new tion of the crystalline material from each crystal to establish a plurality of slabs each having a prepared connecting face which extends parallel to the X and Z orthogonal axes of the original crystal, orienting said crystal slabs so that the X, Y, and Z axes of each crystal slab is parallel to the X, ":Z, and Z axes of each other crystal slab and so that the prepared faces are parallel and facing each other, connecting said crystal slabs together to form a composite slab which is Wider in the direction of the Y axis than a single slab, cutting said composite slab in a direction at an angle to said Y and Z axes to establish a composite crystal plate having crystalline material from more than one oi said plurality of crystals, and treating said composite crystal plate to establish a crystal unit.

5. The process oi making an expander piezoelectric crystal plate comprising the steps of connecting two or more slabs of crystallinematerial of the Rochelle salt type together to establish a composite slab which has a greater dimension in one direction than a single slab has, and cutting said composite slab to establish a composite crystal plate which is longer in one of the direc= tions of its expansion and contraction than can be made by one cut of a single slab.

6. An expander piezoelectric plate comprising a first portion from a first crystal, a second portion from a second crystal, and cement means between edge faces of said first and said second portions and joining said two portions together with their like crystallographic axes extending in the same directions, said joint lying in the plane oi! the X--Z axes of the said two portions of crystalline material.

7. An expander piezoelectric plate comprising a first portion from a first crystal slab having X, Y, and Z orthogonal axes, a second portion from a second crystal slab having X, Y, and Z orthogonal axes, and cement means between edge faces of said first and said second portions and joining said two portions together with their X, Y, and Z orthogonal axes extending, respectively, in the same directions, said joint lying in the plane of the X--Z axes of the crystalline material and substantially perpendicular to the Y orthogonal axis thereof.

8. An expander piezoelectric crystal unit comprising a first expander portion from a first crystal, a second expander portion from a second crystal, cement means having a greater coefficlent of electrical conductivity than said crystalline material between said first and said second portions and joining said two portions together, electrode means in association with said crystal portions and extending across said cement joint, insulating means between said electrode means and said crystal portions at said joint, and lead means connected to said electrode means and adapted to connect said crystal unit in an electrical circult.

9. A piezoelectric crystal unit comprised of two portions of crystalline material joined together by cement having a greater coemcient of electrical conductivity than said crystalline material, two electrodes engaging said crystal unit, one on each of two electrode races thereof, and adapted to have a varying electromotive force therebetween, insulating means between said electrodes and said crystalline material at the location of said joint, and lead means connected to said electrodes and adapted to connect said piezoelectric unit in an electric circuit.

The process of making a Rochelle salt crystal unit comprising the steps of: providing a plurality of Rochelle salt crystal slabs, orienting said plurality of slabs so that their like axes extend in the same directions, connecting said plurality of slabs together to form a composite slab, cutting said composite slab to establish at least one composite plate of a size larger than could have been obtained by a single cut of one crystal slab, and treating said composite plate to establish a Rochelle salt crystal unit.

11. The process of making a Rochelle salt crys= tal unit comprising the steps of: providing a plurality of Rochelle salt crystals, removing a portion of each of said crystals to establish a plurality oi 8 crystal slabs each having a connecting face.

orienting said plurality of crystal slabs so that their like axes extend in the same directions, connecting said slabs together face to face to form a composite crystal slab, cutting said composite crystal slab to establish a composite crystal plate of a size larger than could have been obtained by a single cut of one crystal slab, and treating said composite crystal plate to establish a Rochelle salt crystal unit.

12. The process of making a Rochelle salt crys= tal -unit comprising the steps of: providing a plurality of Rochelle salt crystals of piezoelectrically active crystalline material each having first, sec- 0nd, and third orthogonal axes, removing a portion 0! the crystalline material from each crystal to establish a plurality of slabs each having a prepared connecting face which is parallel to said third orthogonal axis, orienting said plurality of crystal slabs so that each of said first, second, and third orthogonal axes is parallel to each of its like axes and so that the connecting faces lie in a position from which they can be connected together, applying a cement to one or more of said connecting faces, pressing said connecting faces together to establish a composite crystal slab of a large size, cutting said composite crystal slab at an angle to two of said orthogonal axes to establish a composite crystalplate having crystalline material from more than one of said plurality of crystals, and treating said composite crystal plate to establish a Rochelle salt crystal unit.

13. The process of making a crystal unit com prising the steps of: providing a plurality of crystal slabs, orienting said plurality of crystal slabs so that their like axes extend in the same directions, connecting said plurality of crystal slabs together to form a composite slab, cutting said composite slab to establish at least one composite expander crystal plate of a size larger than could have been obtained by a single cut of one crystal slab, providing a second composite expander crystal plate, orienting said two composite expander crystal plates so that for a given electrical field one tends to expand in one direction and the other tends to contract in the same direction, connecting said two oriented composite expander crystal plates together, and treating said connected plates to establish a multiplate flexing crystal unit.

14. A process as set forth in claim 13 in which the crystalline material is Rochelle salt and the said out is at an angle of substantially 45 degrees to the Y--Z orthogonal axes of the crystalline material. v

15. A ndultiplate flexing crystal unit comprising, in combination; a first portion of piezoelectrio crystalline material having a first orientation with respect to the orthogonal axes of the said material, a second portion of piezoelectric crystalline material having the same orientation with respect to the orthogonal axes of the said material as said first portion, means for connecting said two portions together in end-to-end relationship to establish a first long composite crystal plate, a third portion of piezoelectric crystalline material having a different orientation with respect to the orthogonal axes of the said material than said first and second portions have, a fourth portion of piezoelectric crystalline material having the same orientation with respect to the orthogonal axes of the said material as said third portion, means for connecting said third and fourth portions together in end-to-end relationship to establish a second long composite crystal late, means for connecting said first long compo'site crystal plate to said second long composite crystal plate, said two plates being oriented so 17. In a piezoelectric crystal element, plate i means of crystalline material adapted to expand and/or contract upon the application of an electrical potential between two electrode means which are in engagement with and extend over the surface area of spaced-apart electrode faces of said plate means, said plate means comprising at least one plate formed of two pieces of piezoelectric material connected together with the directions of the three orthogonal axes in each of said two pieces extending, respectively, in the same directions and with said electrode means extending across said joint, and insulating means between said electrode means and said plate means only substantially at said joint between said two pieces of piezoelectric material, whereby upon the application of an electrical potential between said two electrode means said insulating means helps to prevent electrical breakdown through said joint.

18. In a piezoelectric crystal element as set 30 Number both said plates only substantially at said joints 86 in said plates.

aaeaeoe id 19. A piezoelectric multiplate assembly comprising a first plate of crystalline material adapted to expand upon a suitable electrical potential being applied thereto in a given direction with respect to the crystallographic axes thereof, a second plate of crystalline material of substan tially the same size and shape as said first plate and adapted to contract upon said same electrical potential being applied thereto in said same given direction, said plates being connected together in registering iace-to-face relationship with the direction Oil the electrical axis in the plane of the connecting laces, each of said plates lacing formed of two pieces of crystalline material connected together with a joint having lower dielectric strength than the dielectric strength of said crystalline material, spaced electrodes on the faces of said plates which are perpendicular to the said electrical axis and extending across said joints in said two plates, and insulatinw means positio'ned between said electrodes and said crystalline material at the locality of said joints.

FRANK MASSA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IEN'I'S Name Date Re. 20,680 Sawyer Mar. 29, 1938 1,688,694 Ellis Oct. 23, 1928 1,766,043 Nicolson June 24, 1930 2,126,438 Williams Aug. 9, 1938 2,139,469 Sachse Dec. 6, 1938 

